This invention relates to a thermal recording device.
Hitherto, in thermal recording devices for performing recording by the use of heating elements arranged so as to cover entirely the width of a recording paper, a so-called density gradation process is generally employed to perform multi-grade recording in which the density of each dot itself is varied.
According to the foregoing process, each picture element is recorded by the use of one dot, so that although the number of heating elements per unit length can be set small, a variation of print density in an intermediate density range is large and hence the number of grades cannot be made larger than 16.
Further, the heating elements are divided into a plurality of blocks and driven in a mode of time-sharing. Since the recording of one line is commenced after the print data of the respective picture elements are always written in a shift register through its least significant bit position, the data must be transferred through non-recording blocks up to a block which has to effect recording. Consequently, the data transfer takes much time and a recording speed is decreased.
The objects of the present invention are to enhance a data transfer speed and to realize a variety of gradation.